Tryptophan is a hydrophobic, aromatic amino acid which serves important functions in enzyme active sites and in other protein binding sites. Many proteins bind large hydrophobic and aromatic molecules such as porphyrins, and tryptophan is involved in some of the binding sites. However, little detail concerning the molecular environment of the bound molecules in membrane proteins is available because crystal structures for most membrane proteins are not yet available. Chlorophyll binding proteins from bacteria are examples of such proteins. Chlorophyll binding proteins are responsible for capture and transfer of light energy in photosynthesis. The amino acid sequences of the proteins and rates of energy transfer are known, making them ideal candidates for characterization of the protein binding sites. By chemically modifying the aromatic amino acid tryptophan, we will alter these amino acids within the chlorophyll binding proteins. We will test whether the binding of chlorophyll and the activity of the protein in energy transfer have been changed. A spectrophotometric which will be used to detect changes in the binding of chlorophyll and to quantitate these changes will be purchased. In addition to chemical modification reactions and spectrophotometric assays, protein purification and qualification procedures will be used in this research. Chlorophyll binding proteins provide the environment required to promote energy transfer between different pigment molecules and ultimately to the photochemical reaction center, where the oxidation-reduction reactions of photosynthesis begin. By improving our understanding of how tryptophan functions in these proteins, we will improve our understanding of how these energy transfer processes occur with high efficiency in photosynthesis, as well as our general understanding of the role of hydrophobic binding sites in proteins.